Method and Apparatus for Filling a Tank with a Cryogenic Liquid

ABSTRACT

The invention relates to a method for filling a tank with a cryogenic liquid from a storage unit, a filling process during which a part of the cryogenic liquid is transformed into a gas phase in the tank, and in which, during the filling, at least part of the gas thus formed is discharged, characterized in that the method comprises providing a filling station containing a first channel which connects the storage unit to the tank and enables the transfer of cryogenic liquid from the storage unit to the tank, and a second channel which connects a gas outlet of the tank to the filling station and makes it possible to transfer the gases to be discharged from the tank to the filling station, where said gases will be discharged to the outside, the station comprising a means for detecting the presence of cryogenic liquid in the gas transferred to the station, the detection information being transmitted to a unit for acquiring and processing data, inside or outside the station, suitable for automatically stopping the filling apparatus when the tank is considered to be full.

The present invention relates to methods for filling a container or tank with a cryogenic liquid such as liquid nitrogen, from a primary container or storage unit, said filling operation exploiting a difference in pressure and gravity between the storage unit and the tank.

The invention is particularly concerned with filling tanks present in trucks used to transport and distribute heat-sensitive products, such as pharmaceuticals and food products.

One of the techniques employed in this type of truck (called indirect injection) uses one (or more) heat exchangers (for example simple coils), conveying a cryogenic fluid, the chamber also being equipped with an air flow system (fans) making said air contact the cold walls of the heat exchanger, thereby serving to cool the air inside the cold chamber of the truck, the cryogenic fluid supplied to the heat exchanger or exchangers originating from a tank of cryogenic fluid conventionally located under the truck.

One of the problems arising here stems from the fact that during the filling operation, a non-negligible portion of the cryogenic liquid is converted to the gas phase in the tank. Thus, to preserve the requisite pressure difference between the storage unit and the tank, the gas must be discharged from the tank via a gas outlet.

The valves controlling, on the one hand, the cryogenic liquid feed to the tank and, on the other hand, the gas outlet of the tank, must be open while the tank is being filled, and closed at the end of the filling operation. The end of the filling operation may be recognized automatically by suitable means or else manually by the operator.

As will be understood, it is necessary to have, between the storage unit and the tank, elements for controlling the flow rate and the opening/closure (valves) of the channel for supplying the tank with cryogenic liquid. Thus, in the following description, all of these elements (their type, assembly, operation) are comprehensively referred to as “filling station”.

At present, this filling operation is generally managed by one of the following procedures:

a) In a first approach, the filling station comprises a single manual valve. A hose for transferring liquid nitrogen connects the filling station (that is to say, the manual valve) with the tank. The gas created during injection is discharged from the tank to the exterior in an uncontrolled manner. The operator decides to terminate the filling operation when he visually detects liquid particles in the gases discharged from the tank. After stopping the filling operation, the operator purges the hose.

The drawbacks of this solution, which is basically empirical, can be summarized as follows:

-   -   the solution is not ergonomic: all the sequences require manual         action by the operator, and it is he who judges when to stop the         filling;     -   the risk of committing handling and assessment errors is high,         for example:         -   i) closure of the valve before the tank is completely             filled,         -   j) no closure or late closure of the valve after complete             filling, causing liquid nitrogen to splash outside the tank,             incurring the risk of burns to the persons present, as well             as losses of cryogenic liquid,         -   k) no hose purge: risk of hose bursting/whiplash;     -   the discharge to the exterior of the gas formed is not         controlled: the tank is consequently not pressurized following         the end of the filling operation. It must therefore be         pressurized for a future use in an application requiring an         immediate minimum pressure.

In fact, in the case of such a manual filling operation, the gas outlet line of the tank is opened or closed using a manual valve present on the tank. Said valve allows for complete opening/closure. During the filling operation, the manual valve is open, the gas is discharged and the tank is then at atmospheric pressure.

If we consider an application of the use of liquid nitrogen from the tank, requiring a minimum pressure of 2 to 2.5 bar, it is clear that this manual procedure is unable to deliver said minimum pressure. It would therefore be necessary to wait for the heat intake to raise the pressure in the tank, and in practice it is necessary to install a pressurizing system (vaporizer).

b) Another type of approach has been proposed, in which the filling operation is stopped when the tank is full, for example by adding elements to the tank such as a solenoid valve or a temperature probe, and by transmitting data by electrical cable from these elements to the station:

-   -   the ergonomics of this approach are only slightly improved         compared to the preceding ones, because many sequences are still         manually controlled by the operator;     -   this approach requires an electrical connection between the         station and the tank, which may ultimately prove to be a weak         point in such an environment (very low temperatures, risks of         detaching the cable, and the need to connect the cable to the         tank, which represents a loss of ergonomics).

It is therefore clear that a novel technical solution must be proposed, one that provides better ergonomics (automating all or part of the operations), limiting the risks of error indicated above, and serving, whenever necessary, to reach the minimum pressure for subsequent use of the tank concerned, without the need to employ a pressurizing system.

As shown in greater detail below, the present invention proposes a novel filling procedure, whose essential feature is the fact that the gas discharged from the tank is not “lost” but, on the contrary, recovered and controlled, by the fact that a gas discharge channel from the tank connects the tank to the filling station, where this gas discharged from the tank is treated in terms of process control.

In brief:

-   -   a first channel (fully or partly flexible) connects the storage         unit to the tank, via the filling station, and serves to         transfer cryogenic liquid from the storage unit to the tank;     -   a second channel (fully or partly flexible) connects the gas         outlet of the tank to the filling station and therefore         transfers these gases to the filling station where these gases         are “processed”, that is to say treated in terms of process         control;     -   as shown below in greater detail, the control of the gas return         to and in the filling station by means which are more or less         complete and extensive according to the various embodiments of         the invention, has highly significant advantages, and in         particular:     -   1. by using suitable control means, the filling can be stopped         automatically when the tank is full, by detecting the presence         of liquid nitrogen in the gas return line (for example, by a         temperature probe indicating a drop in temperature in the gas         return line due to the temperature difference between the         cryogenic liquid and its gas);     -   2. for example, by the presence of a back pressure regulator on         the gas return line, a desired pressure level can be maintained         in the tank at the end of the filling operation, which is         extremely advantageous in order to avoid having to repressurize         the tank after the filling operation in the case of a subsequent         use of the tank requiring a minimum pressure (as mentioned         above);     -   3. optionally, but also advantageously, it is possible to         diminish the noise level in the station by installing a silencer         (for example, on the gas outlet from the station to the         exterior);     -   4. any liquid nitrogen flow on the ground is completely         prevented since the gas outlet of the station can be protected         by a cubicle in which the entire filling station is installed;     -   5. as shown below, the purge of the hoses can be initiated         automatically at the end of the filling operation;     -   6. automatic recognition of the tank can be arranged, which can         be highly advantageous, in particular for obtaining traceability         of the filling events (last filling date, quantity supplied,         etc.);     -   7. proper filling management according to the maximum acceptable         working pressure (MAWP) of the tank: by monitoring the actual         pressure in the tank, which can be done by using a pressure         sensor in the filling station on the gas return line and/or on         the liquid nitrogen line;     -   8. also worth mentioning is the possibility that the gas can be         discharged by remote control, thereby limiting the risks of         anoxia;     -   9. as will be understood, in comparison with the prior art         solution, which proposed to add elements such as a solenoid         valve, a temperature probe, etc. to the tank, and to transmit         data by electrical cable between these elements and the station,         the present invention does not require these control elements on         the tank, or even on a plurality of tanks if such exist, and the         station alone assembles together the necessary elements in a         single step, clearly offering an undeniable cost benefit.

The present invention accordingly relates to a method for filling a tank with a cryogenic liquid from a storage unit, during which filling operation part of the cryogenic liquid is converted to the gas phase in the tank, and in which, during the filling, at least part of the gas thus formed is discharged, which method comprises providing a filling station through which there passes a first channel, which connects the storage unit to the tank and allows the transfer of cryogenic liquid from the storage unit to the tank, and where there terminates a second channel which connects a gas outlet of the tank to the filling station and makes it possible to transfer the gases to be discharged to the filling station, where said gases will be discharged to the exterior, the station comprising means for detecting the presence of cryogenic liquid in the gas transferred to the station, and the detection data being transmitted to a data acquisition and processing unit, inside or outside the station, suitable for automatically stopping the filling operation when the tank is considered to be full.

As clearly appears to a person skilled in the art, this “full tank” concept must be understood as relating to the position of the gas return tube in the tank. In practice, filling “to the brim” is never permitted, and a free space (for example 5% of the tank volume) is always left, which is necessary for movement and vaporization of the liquid. The tank is accordingly considered to be “full” when it is filled for example to 95% and, because of the filling dynamics, liquid will escape toward the station upon approaching the 95% level, which, according to the invention, will cause the filling to stop. A person skilled in the art is therefore familiar with these “full tank” concepts.

According to one of the embodiments of the invention, said detecting means consist of a temperature probe located on said second channel, indicating an abnormally high drop in temperature in the gas transferred to the station.

As will be clearly apparent to a person skilled in the art, and in order to illustrate this question of a temperature drop, the drop in temperature recorded by the station in the gas return line will obviously vary according to the situations and conditions. For illustration, if we consider the example of a liquid nitrogen tank at 2-2.5 bar, the temperature of the cold gas is close to about −150° C., and when liquid touches the temperature probe, the temperature measured by the probe drops to about −180° C.

In practice, in the early moments of filling, the gas is “warm” (ambient temperature) and its temperature will steadily fall as the filling proceeds, until reaching about −150° C.

Therefore, when the tank is “full”, for example to the 95% level, liquid will leave the tank and flow toward the probe of the station, initially in what can be described as “small jets”, and these preliminary small jets cause the temperature to drop to about −160/−165° C., triggering the automatic interruption of the filling operation.

According to the invention, the second channel, connecting a gas outlet of the tank to the filling station, is equipped with a back pressure regulator, said back pressure regulator being set to an upstream pressure setpoint serving to reach a minimum pressure in the tank, which is necessary for a subsequent use of the tank concerned, without the need to employ a pressurizing system.

The invention may also adopt one or more of the following technical features:

A/ the connections between the storage unit and the tank on the one hand, and between the gas outlet of the tank and the station on the other hand, are made by a system of two male/female double couplers:

-   -   a first double coupler (“storage unit side”) where a flexible         portion of the first channel connecting the storage unit to the         tank terminates, and from which a flexible portion of the second         channel connecting the gas outlet of the tank to the station         issues;     -   a second double coupler (“tank side”) where a flexible portion         of the second channel connecting the gas outlet of the tank to         the station terminates, and from which a flexible portion of the         first channel connecting the storage unit to the tank issues;     -   one of the two double couplers (“tank side”) being of the male         type while the other of the double couplers is of the female         type, the connection of the two double couplers ensuring the         continuity of fluids in the first channel on the one hand,         connecting the storage unit to the tank, and in the second         channel on the other hand, connecting the gas outlet of the tank         to the station.

B/ said second double coupler “tank side” is in fluid connection with the upper part of the tank.

C/ a purge line is provided, equipped with a solenoid valve, said purge line being connected in its upstream portion to said first channel connecting the storage unit to the tank, and to which the second channel which transfers the gases to be discharged to the filling station is advantageously connected, thereby allowing the discharge of the gases discharged from the tank via this line to the exterior (it should be understood that the purge lines of the liquid line, and the discharge to the exterior of the gases transferred to the station, could also be two separate and independent lines in the station).

D/ According to one of the embodiments of the invention, at least a portion of said first channel connecting the storage unit to the tank is purged after the filling is stopped, by the fact that after a predefined time t1 the portion of first channel to be purged is purged by opening a solenoid valve located on a purge line which is connected in its upstream portion to said first channel connecting the storage unit to the tank.

E/ According to one of the embodiments of the invention, the flexible portion of the first channel connecting the storage unit to the first double coupler is purged, using one of the following techniques:

-   -   after a predefined time t1, the hose is purged by opening a         solenoid valve located on a purge line which is connected in its         upstream portion to said first channel connecting the storage         unit to the tank;     -   a sensor is provided for detecting the correct positioning of         said first double coupler on a fastening element present on the         filling station (for example such as a “parking plate” next to         the filling station) and the fastening of said first double         coupler to said element automatically initiates the purging of         the flexible portion of the first channel connecting the storage         unit to the first double coupler.

F/ the tank is present on a truck used to transport and distribute heat-sensitive products, such as pharmaceuticals and food products.

According to optional but advantageous embodiments of the invention, the invention may have one or more of the following features:

-   -   the installation may comprise a second parallel line, for         transferring cryogenic liquid from the storage unit to the tank,         for filling tanks in which the maximum service pressure is         reduced, the second line comprising a calibrated orifice to         limit the maximum pressure acceptable to the tank;     -   advantageously, the tank may be equipped with elements for         automatic recognition of the tank to be filled, for example         electronic tags of the RFID type featuring passive or active         technology, but other recognition modes are feasible, including         a manual choice of the tank to be filled by the operator on a         user interface (“validation”).     -   advantageously, a sensor is provided for detecting the correct         positioning of the double coupler on a fastening element present         on the filling station (for example, a sort of “parking plate”         next to the filling station) and the fastening of the double         coupler to said element automatically initiates the purging of         the hoses scheduled to take place at the end of the filling         operation.

And according to one possible embodiment of the invention, the detection of the absence of the double coupler on the fastening element (parking plate, for example) may be used to authorize the start of the filling and therefore refuse said start when the coupler is still on its plate.

Other features and advantages will appear from the following description, of exemplary embodiments of the invention, provided in particular with reference to the appended drawings in which:

FIG. 1 is a schematic overall view of an installation for filling the tank of a refrigerated transport truck, serving to show the presence of the filling station between the storage unit and the tank;

FIG. 2 is a detailed view of the contents of the filling station according to one embodiment of the invention.

FIG. 1 has two parts:

-   -   in the upper part, a general view serving to show the liquid         nitrogen storage unit, the filling station of the invention, the         food transport truck equipped with its liquid nitrogen tank, and         a non-detailed view of the two lines for supplying the tank with         liquid nitrogen and the return of the gas discharged from the         tank to the station, two double couplers ensuring the continuity         of fluids;     -   in the lower part, the view of the two channels used to supply         the tank with liquid, and to discharge the gas formed in the         tank to the station, is more detailed, showing clearly the         presence of the two male/female double couplers:     -   a first double coupler (“storage unit side”) where a flexible         portion of the first channel connecting the storage unit to the         tank terminates, and from which a flexible portion of the second         channel connecting the gas outlet of the tank to the station         issues;     -   a second double coupler (“tank side”) where a flexible portion         of the second channel connecting the gas outlet of the tank to         the station terminates, and from which a flexible portion of the         first channel connecting the storage unit to the tank issues;     -   the connection of the two double couplers ensuring the         continuity of fluids in the first channel on the one hand,         connecting the storage unit to the tank, and in the second         channel on the other hand, connecting the gas outlet of the tank         to the station, the second double coupler (“tank side”) being in         fluid communication with the upper part of the tank.

With reference to FIG. 2, we shall now examine in greater detail the contents of the filling station of the invention, according to a very complete embodiment.

FIG. 2 shows the liquid nitrogen tank 1 and, for the embodiment exemplified here, the contents of the filling station 5, and the lines passing through it or terminating therein: the cryogenic liquid feed line (to 2), the gas return line (from 3) and the various equipment attachments present on said lines.

For better legibility, the two connections of the two double couplers have been separated in space (reference 4) in this figure, but as will be clearly apparent to a person skilled in the art, these two double couplers must be understood as a storage-unit-side first double coupler, for example a male double “connector”, and a tank-side second double coupler, for example a female “housing”, i.e. double channel for accepting the opposite, male, double connector.

The double couplers have been positioned outside the area symbolizing the station, but this is a subsidiary point, for definition; these double couplers can be considered as being optionally part of the station, without really modifying the scope of the present invention.

In the liquid-nitrogen first channel, the presence of a solenoid valve 10 and a pressure sensor 12 can be recognized.

In the gas-return second channel, the presence can be recognized of a solenoid valve 20 and a back pressure regulator 21 (whose role has been broadly explained above), as well as the presence of a temperature sensor 23 (whose essential role has also been explained above in the present description) and a pressure sensor 22.

FIG. 2 also serves to better show one of the aspects of the invention already explained, that is to say the means for discharging to the exterior the gases discharged from the tank and transferred to the station: a purge line 30 is present, for example connected in its upstream portion to the cryogenic nitrogen channel, to which purge line the gas return channel is connected for this embodiment, said purge line being equipped with a purge solenoid valve 31, and a highly advantageous silencer 33 for this embodiment.

FIG. 2 also shows the presence of manual bypass valves on each of the lines, valves 11, 23 and 32, whose presence is obviously only optional, but which are designed for emergency operation during a limited period in case of station malfunction.

It should be noted that for reasons of legibility, the figure does not show the second parallel line, for transferring cryogenic liquid from the storage unit to the tank, for filling the tanks whose maximum service pressure is reduced, said second line comprising a calibrated orifice for limiting the maximum pressure acceptable to the tank, but it has already been stated above that this possibility is feasible and advantageous.

As we have shown, the temperature probe 23, installed on the gas return line in the filling station, serves to detect—via an abnormally high drop in temperature of this gas return line—the presence of liquid nitrogen in the gas return line, indicating a complete filling of the tank. Said detection data is sent to the data acquisition and processing unit present in the station (not shown to avoid cluttering the figure), which unit orders the filling to be stopped (closure of the valve 10, and closure of the valve 20 to prevent a loss of pressure in the tank and its inadvertent degassing).

When the operator uncouples the “storage unit side” double coupler (which can also be called the “station side” double coupler), the two (liquid line and gas line) valve flaps of the coupler are closed and liquid is confined between the valve flap of the liquid line and the solenoid valve 10 on the liquid line. To carry out the purge, the valve 31 on the purge line 30 must be opened and therefore controlled. For illustration, two events can be used to order the opening of this valve 31:

-   -   the station may, for example, detect the presence of the         “storage unit” double coupler which, after uncoupler, is         returned to its fastening support on the station (not shown);     -   the unit may also count the end of a time delay (for example 2         minutes) after it (i.e. the unit) has ordered the filling to be         stopped.

Another eventuality (in very specific cases however) is that before the lapse of the time delay t1, another filling operation must be carried out (for example to fill a second tank present under the truck in the case of high nitrogen requirements): in such a case, it will obviously be useless and superfluous to initiate the intermediate purge, and it is simpler for the operator to disconnect the double coupler of the first tank and reconnect said double coupler to the second tank, and then press a “start” button to start said second filling, the purge only being carried out after the second filling has been stopped.

Obviously, this description of two sequential filling operations of two tanks would also apply to cases, which are admittedly even more infrequent, of more than two tanks and hence more than two sequential filling operations to be carried out, but the principle thereof is nevertheless quite clear from the above description.

Thanks to the presence of the back pressure regulator 21, the outgoing gas is returned to, and controlled in, the filling station, thereby serving to preserve a minimum pressure in the tank (for example 2 bar), which is very useful in certain subsequent applications requiring a minimum pressure, and not simply atmospheric pressure, and according to the invention the solenoid valve 20 can be controlled according to the pressure required in the tank.

As will be understood, the manual filling operations according to the prior art do not allow such control, because in the case of such a manual filling operation, the gas outlet of the tank is opened or closed by means of a manual valve on the tank. Said valve allows complete opening/closure. During the filling operation, the manual valve is opened, the gas is discharged and the tank is thus again under atmospheric pressure, which does not serve to deliver the minimum pressure required by certain subsequent uses (for example 2 to 2.5 bar for the “direct injection” technique in refrigerated truck transport).

According to this prior manual procedure, it is then necessary to wait for heat inputs to raise the pressure in the tank, or to have a pressurizing system (vaporizer).

For illustration, an example is provided below of an automatic filling procedure of a tank according to the invention.

1) Connection by the operator of the double coupler of the filling station to the tank-side double coupler to be filled. The tank cavity is now connected via the hoses with the filling station and its control elements (valve, pressure sensor, temperature sensor, etc.).

2) Recognition of the tank to be filled and consideration of its maximum acceptable pressure.

3) The operator presses a button so as to initiate the filling operation.

4) The pressure in the hoses is checked so as to check the proper connection of the tank (via sensor 12).

5) If the hoses are properly connected: opening of the valve 10 on the liquid nitrogen line.

6) During the filling operation, the liquid pressure (12) is monitored as an indicator of the pressure in the tank and the valve 10 on the liquid nitrogen line is closed in case of excessive pressure: the sensor 12 serves to ensure that the pressure in the tank does not exceed a safe pressure, and therefore causes the closure of the valve 10 as required.

7) During filling: opening/closing cycles of the valve 20 on the gas return line to control the pressure in the tank and thereby also increase the filling rate.

As a first exemplary application, a tank A may need a working pressure of 2.5 bar, while in a second exemplary application a tank B needs 1 bar only.

The back pressure regulator 21 and the solenoid valve 20 on the gas return line provide a maximum flow rate for the gas outlet while preserving the minimum pressure required.

8) The detection of an abnormally low temperature on the gas return line (as already explained above) indicates the presence of liquid nitrogen in the gas return line and the complete filling of the tank. The valve 10 is consequently closed, and also the valve 20, and the operator is informed of the end of filling by any suitable (acoustic, visual) signal.

It is clear that in precise and exceptional cases, particularly a safety situation, the signal in question may allow the operator to avoid relying on the automatic stopping of the filling operation by the station, and instead to order the filling operation to be stopped himself, for example by pressing an appropriate button, but it is clear that above all, the merit of the present invention resides in the fact that the discharged gases are not lost, but are returned to a process control station, thereby serving to limit human actions, which are such sources of errors and malfunctions.

9) After a predefined time t1 (for example 2 minutes), the liquid nitrogen transfer hose is purged by opening the solenoid valve 31 connecting the liquid nitrogen line to the gas outlet of the station. The purge can also be initiated when the presence of the “station” double coupler is detected on the parking plate of the station.

As will have been understood, the fact of performing this dual “filling/gas return” operation by a male double coupler on a female double coupler is optional, certainly highly advantageous but still optional, and it is also possible, without departing from the scope of the present invention, to connect two well-separated channels (and couplers) issuing from the station to two well-separated couplers on the tank or in fluid communication with said tank.

As already mentioned, the data acquisition and processing unit is preferably located within the station, for obvious reasons of convenience of wiring, but, without departing from the scope of the invention, the unit could equally well be located outside the station, and the required cables would then be drawn between the unit and the station. 

1-14. (canceled)
 15. A method for filling a tank with a cryogenic liquid from a storage unit with a filling station, during which filling operation part of the cryogenic liquid is converted to the gas phase in the tank, and in which, during the filling, at least part of the gas thus formed is discharged to an exterior of the filling station, said method comprising the steps of: providing a filling station comprising a first channel which connects the storage unit to the tank and allows a transfer of cryogenic liquid from the storage unit to the tank and a second channel which connects a gas outlet of the tank to the filling station, the second channel allowing transfer of gases, to be discharged, from the tank to the filling station, the station further comprising a temperature probe adapted to detect the presence of cryogenic liquid in the gases transferred to the filling station from the tank and to transmit data indicating said presence to a data acquisition and processing unit; initiating a fill of the tank with cryogenic liquid from the storage unit via the first channel; and automatically stopping the fill of the tank with the data acquisition and processing unit upon receipt of the cryogenic liquid presence data, wherein the second channel is equipped with a back pressure regulator set to an upstream pressure setpoint corresponding to a minimum pressure in the tank necessary for a subsequent use of the tank without a need to employ a pressurizing system on the tank.
 16. The filling method of claim 15, wherein the temperature probe is located on the second channel, the temperature detecting the presence of cryogenic liquid in the second channel by detecting an abnormally high drop in temperature in the gas transferred to the station.
 17. The filling method of claim 15, wherein the first and second channels comprise first and second double couplers: the first double coupler at which a flexible portion of the first channel connecting the storage unit to the tank terminates, and from which a flexible portion of the second channel connecting the gas outlet of the tank to the station issues; a second double coupler at which a flexible portion of the second channel connecting the gas outlet of the tank to the station terminates, and from which a flexible portion of the first channel connecting the storage unit to the tank issues; one of the two double couplers being of a male type while the other of the double couplers is of a female type, connection of the two double couplers ensuring the continuity of fluids in the first and second channels.
 18. The filling method of claim 17, wherein said second double coupler is in fluid connection with an upper part of the tank.
 19. The filling method of claim 15, wherein the filling station further comprises a purge line equipped with a solenoid valve, an upstream portion of the purge line being connected to the first channel; and the purge line is optionally also connected to the second channel thereby allowing a discharge to the exterior of the station of the gases discharged from the tank to the station.
 20. The filling method of claim 19, wherein at least a portion of the first channel connecting the storage unit to the tank is purged after the filling is stopped by the data acquisition and processing unit, by opening the solenoid valve located on the purge line after a predefined time t1.
 21. The filling method of claim 17, wherein the flexible portion of the first channel connecting the storage unit to the first double coupler is purged, by opening the solenoid valve after a predefined time t1.
 22. The filling method of claim 17, wherein: the flexible portion of the first channel connecting the storage unit to the first double coupler is purged by detecting a correct positioning of the first double coupler on a fastening element present on the filling station via a positioning sensor; and the fastening of said first double coupler to said element automatically initiates the purging of the flexible portion of the first channel.
 23. The filling method of claim 15, wherein the tank is present on a truck used to transport and distribute heat-sensitive products pharmaceuticals or food products.
 24. An installation for filling a tank with a cryogenic liquid from a storage unit, during which filling operation part of the cryogenic liquid is converted to the gas phase in the tank, and in which, during the filling, at least part of the gas thus formed is discharged, the installation comprising: a filling station; a first fluid channel passing through the filling station, connecting the storage unit to the tank and allowing the transfer of cryogenic liquid from the storage unit to the tank; a second fluid channel connecting a gas outlet of the tank to the filling station and serving to transfer the gases to be discharged to the filling station; a temperature probe adapted to detect a presence of cryogenic liquid in the gas transferred to the station and send data indicating said presence; a data acquisition and processing unit adapted to receive the presence data from the temperature probe, and upon said receipt, automatically filling of the tank with cryogenic liquid from the storage unit, wherein the second channel is equipped with a back pressure regulator, the back pressure regulator being set to an upstream pressure setpoint serving to reach a minimum pressure in the tank that is necessary for a subsequent use of the tank without a need to employ a pressurizing system.
 25. The filling installation of claim 24, wherein the temperature probe is located on said second channel and is adapted to detect an abnormally high drop in temperature in the gas transferred to the station indicating the presence of the cryogenic liquid in the second channel.
 26. The filling installation of claim 24, wherein: the first and second channels comprise first and second double couplers; the first double coupler at which a flexible portion of the first channel connecting the storage unit to the tank terminates and from which a flexible portion of the second channel connecting the gas outlet of the tank to the station issues; the second double coupler at which a flexible portion of the second channel connecting the gas outlet of the tank to the station terminates and from which a flexible portion of the first channel connecting the storage unit to the tank issues; and one of the double couplers being of a male type while the other of the double couplers is of a female type, connection of the two double couplers ensuring continuity of fluids in the first and second channels.
 27. The filling installation of claim 24, wherein said second double coupler is in fluid connection with the upper part of the tank.
 28. The filling installation of claim 24, further comprising a purge line equipped with a solenoid valve, upstream portion of the purge line being connected to the first channel, wherein the second channel which transfers the gases to be discharged to the filling station is optionally connected to the purge line thereby allowing discharge to an exterior of the station via the purge line of the gases discharged from the tank and transferred to the station.
 29. The filling installation of claim 24, wherein the tank is present on a truck used to transport and distribute heat-sensitive pharmaceuticals or food products. 